In a semiconductor fabricating process, a photolithography process has been employed. In the photolithography process, in order to form a desired circuit pattern, a resist film is formed on a substrate such as a semiconductor wafer by coating the substrate with photoresist, and the resist film is exposed to light by using a certain circuit pattern and is developed. In general, the photolithography process is performed by a processing system in which an exposure apparatus is connected to a coating and developing apparatus.
In the photolithography process, there has been generally known a spin coating method of forming the resist film onto a surface of the substrate through centrifugal force by supplying a resist solution as a chemical liquid onto a central portion of the surface of the substrate while spinning the substrate about a vertical axis thereof. In the spin coating method, in order to supply a certain amount of resist solution onto the surface of the substrate, a chemical liquid supply method (system) using a constant pressure pump has been employed.
In the conventional spin coating method, there has been known a chemical liquid supply system (see, for example, Patent Document 1). This chemical liquid supply system includes a chemical liquid passageway; a chemical liquid pump; an operation gas supply device; a first opening/closing valve and a second opening/closing valve. The chemical liquid passageway connects a chemical liquid tank for storing therein a resist solution and a chemical liquid discharge nozzle. The chemical liquid pump, the operation gas supply device, the first opening/closing valve and the second opening/closing valve are provided on the chemical liquid passageway. The chemical liquid pump is partitioned into a pump chamber and an operation chamber by a flexible member. Here, a volume of the pump chamber is varied depending on the change in internal pressure of the operation chamber. With this configuration, the chemical liquid pump performs suction or discharge of a chemical liquid (resist solution) according to the volume change of the pump chamber. The operation gas supply device supplies an operation gas into the operation chamber of the chemical liquid pump while adjusting the pressure thereof. The first opening/closing valve and the second opening/closing valve are respectively provided at a first side and a second side of the chemical liquid pump on the chemical liquid passageway. With this valve configuration, a pressure value of the operation gas supplied from the operation gas supply device is detected, and the pressure value of the operation gas is set depending on types of chemical liquids or other conditions. Then, the chemical liquid supply system controls the discharge flow rate of the chemical liquid by using the detected pressure value and the set pressure value.
In this chemical liquid supply system, in order to prevent introduction of impurities into the resist solution to be discharged, a filter is provided at the first side of the chemical liquid pump on the chemical liquid passageway.
Patent Document 1: Japanese Patent Laid-open Publication No. 2007-110004 (Claims)
Patent Document 1 describes that the pressure value of the operation gas is detected when the operation gas is supplied from the operation gas supply device, and the discharge flow rate of the chemical liquid is controlled based on the detected pressure value and the previously set pressure value. Patent Document 1, however, does not disclose anything about the control of an exhaust pressure (exhaust flow rate) of the operation gas when the chemical liquid is sucked in by the chemical liquid pump, that is, when the chemical liquid is replenished.
In Patent Document 1, when the chemical liquid is replenished to the pump chamber of the chemical liquid pump after discharging the previously supplied chemical liquid, if the first opening/closing valve is opened and the operation gas in the operation chamber is exhausted, there is generated a pressure difference between an upstream side and a downstream side of the first opening/closing valve, i.e., between the pump chamber and the operation chamber. As a result, excessive pressure fluctuation, i.e., overshoot occurs when the replenishment of the chemical liquid is started. This is also caused by variation of an amount of the chemical liquid remaining in the chemical liquid tank. The overshoot that occurs when starting the replenishment of the chemical liquid into the chemical liquid pump is a common problem in a chemical liquid supply system using a fixed-quantity pump.
Once the overshoot occurs, a flow rate of the chemical liquid replenished into the pump chamber of the chemical liquid pump increases, and a flow rate thereof also becomes faster. Accordingly, a filtering rate of the filter also increases, and there is a concern that impurities or foreign substances in the chemical liquid pass through the filter without being filtered. Further, while the chemical liquid containing impurities passes through the chemical liquid pump and reaches a chemical liquid discharge unit after passing through the filter, particles may be generated and discharged from the chemical liquid discharge unit onto a surface to be coated with chemical liquid. Especially, under the recent trend, there is a tendency to reduce a discharge amount of resist. Accordingly, in order to meet demand for the small discharge amount of resist, the filtering rate of the filter needs to be precisely controlled. In this regard, an adverse effect resulting from the overshoot may not be overlooked.